The invention relates generally to universal serial buses in computers, and more specifically to regeneration of a synchronization signal in a universal serial bus device or repeater.
A Universal Serial Bus (USB) is a common feature of today""s computers, and provides a flexible and inexpensive interface through which the computer can exchange data with peripheral devices.
USB is an industry standard bi-directional interface system, developed with a focus on connectivity to voice and compressed video sources such as telephone applications, and with a focus on ease of use for the end user. The system is also flexible in the data it receives, including the ability to receive isochronus data that is provided at an arbitrary or self-clocking rate such as sampled audio signals.
Because of its flexibility, the USB interface is also suitable for use with traditional interface devices such as keyboards, mice, printers and scanners. The USB interface is a bus interface, enabling attachment and use of multiple devices to a single USB interface port. An added benefit to using a USB interface is the ability of USB devices to self-configure or to operate as plug-and-play devices, eliminating the need for consumers to understand and configure multiple ports such as serial and parallel ports, keyboard ports, mouse ports, and joystick interfaces.
Devices on a USB bus are attached via a single standard interface connection, and electrical details such as bus termination are isolated from the end user. USB devices can be dynamically attached or configured, and can self-identify and configure themselves upon connection to a computer system. The bus supports concurrent operation of many devices at a time, and is designed with a low bus protocol overhead to enable high data utilization of the available bus bandwidth. The bus protocol is designed to be flexible, and supports a wide range of packet sizes and a wide range of device buffering options and latency with integrated flow control.
Each USB bus system has a host, which is typically an interface adapter in a computer system. Each host has one or more hubs, each of which provides connectivity to one or more nodes or devices. Each hub may also provide connectivity to one or more other hubs, which in turn may each provide connectivity to multiple nodes or devices. Each hub is capable of receiving data from the nodes, the host, or from another hub, and is capable of repeating or retransmitting the data to another host or hub on the bus. A series of up to five hubs may separate any particular USB device from the USB host, allowing a large number of devices to be controlled by a single host.
Current USB hubs are designed to repeat or retransmit data before a valid synchronization (sync) signal is detected. This makes these devices somewhat susceptible to noise, or to the risk that random noise will initiate spurious repeater operation. A revision of the USB specification (USB Specification 2.0, under development) requires in some embodiments that devices which receive and repeat USB data signals over the USB bus must wait until receiving a signal indicating the end of a sync signal before enabling a transmitter to repeat data. Such devices have a greater need for the ability to distinguish valid signals from noise than previous generations of USB system devices, due in part to a reduction in data signal voltage from 3.3 volts to 400 millivolts in the USB 2.0 specification. What is needed is a method and apparatus of detecting and retransmitting the sync field in a manner which provides low delay and low gate count.